(696a) Silica-Peg Gel Encapsulation Platform for Isolation of Dormant Cancer Cells

A major barrier to improving treatment of breast cancer is the ability of a subset of tumor cells to leave the tumor early in disease progression and enter a dormant state at other sites in the body. Since most chemotherapies target rapidly growing cells, these dormant cells can evade treatment and remain undetectable within the body for months or even years before reawakening and causing disease recurrence. Our understanding of the basic mechanisms regulating dormancy and reawakening has been severely limited by the lack of in vitro model systems that can maintain cells in a dormant state. To address this need, we have developed a method for encapsulation of cancer cells in highly porous yet stiff silica-PEG (SPEG) gels that physically confine cells, inhibiting their ability to proliferate, while still enabling nutrient transport. Furthermore, the SPEG gels are mechanically reversible (shear-thinning), enabling release of the encapsulated cells without the need for chemical or thermal treatment of the gel. Alamar blue assays demonstrated that following encapsulation, metabolic activity of MCF-7 breast cancer cells, which are known to exhibit dormant phenotypes, decreased to 30% of the initial value by Day 3 and remained constant up to Day 7. In contrast, MDA-MB-468 cells, which are highly aggressive and are not known to transition into dormancy in vivo, exhibited a sharp decrease in metabolic activity, with no activity observed after Day 2. Comparison of post-encapsulation viability of MCF-7, MDA-MB-468 and MDA-MB-231 cells, which are also more proliferative than MCF-7, confirmed the metabolic activity results, with a population of live MCF-7 cells persisting until Day 7, while all MDA-MB-468 and MDA-MB-231 cells were dead by Day 3. Co-staining of Calcein AM with Ki67, a marker of actively cycling cells, indicated that the persisting population of live MCF-7 cells exhibited a significant reduction in Ki-67 expression, which is a hallmark of tumor dormancy. Importantly, the cells resumed proliferation after removal from the gels, indicating that the proliferation-arrested cells were quiescent and not senescent. Taken together, the preliminary data show that the SPEG gel encapsulation platform is a promising tool for identification and analysis of dormancy-capable sub-populations of cancer cell lines through physical inhibition of proliferation. Future efforts are focused on exploring the utility of this platform in understanding mechanisms of dormancy and reawakening as well as in development of clinical diagnostic tools.